Gas dispersion nozzle apparatuses for use in fluidized bed furnaces are required to have the following performances.
(1) They have high heat-resistance and durability
(2) They are capable of uniformly fluidizing a fluidized bed which is comprised of refractory particles in a retort at every temperature, and
(3) They are capable of minimizing the heat flow from the lower portion of the retort.
As one of gas dispersion nozzle apparatuses which have so far been used, there is known an apparatus wherein a dispersion plate made of porous ceramic is fixedly secured by bonding by means of an adhesive below the inner bottom surface of a retort in such a manner that it extends in substantially parallel relationship with the inner bottom surface of the retort so as to define a space between it and the inner bottom surface, and a nozzle apparatus having a nozzle for injecting air or a treating gas is provided in the space defined between the lower surface of the gas dispersion plate and the inner bottom surface of the retort.
The points at issue of this prior art example are: (1) the gas dispersion is liable to break or crack since it is made of ceramic, (2) to maintain the fixing of the gas dispersion plate to the inner side wall surface of the retort, it is necessary to cool down the retort from the outer periphery thereof so as to prevent the melting of the adhesive by heat, thus causing heat losses, and (3) in order to protect the applied adhesive, the internal temperature of the retort must be lowered to 700.degree. C. prior to stopping the fluidization of the fluidized bed, which results in lossess in operation time and heat, etc.
Another prior art gas dispersion nozzle apparatus devised to solve the points at issue of the above-mentioned first prior art example comprises a gas dispersion plate fixedly secured below the inner side wall surface of a retort in parallel with the inner bottom surface thereof to prevent the applied adhesive from melting by heat, and a multiplicity of nozzle tubes mounted, respectively, in a plurality of longitudinal through-holes formed in the gas dispersion plate, each of the nozzle tubes having a plurality of horizontal nozzles located above the dispersion plate.
This second prior art example has also the following points at issue.
(1) Many complicated working processes are required to fabricate the nozzle tubes, thus rendering the cost of the gas dispersion nozzle apparatus expensive.
(2) Because of high pressure losses in the nozzle tubes, provision of a blower having a large capacity is required, and in case it is used in a heat-circulation type fluidized bed, the circulation efficiency thereof is poor.
(3) Since the injection nozzles are located horizontally, fluidizing particles are liable to make an ingress into the nozzles causing frequent clogging of the nozzles with the particles.
(4) Since the gas dispersion plate has a plurality of nozzle tube mounting holes formed therein and supports the weight of the fluidizing particles, the maximum allowable internal temperature of the retort is limited, to 1,100.degree. C., and therefore the apparatus cannot be used at temperatures exceeding it, etc..